Research On The Algorithm And System Of Transient Microwave Near-field Imaging

The rise of Location Based Service(LBS) in the mobile intelligent terminals indicates that the real-time short-range locating and imaging technologies, for example in-door locating, have great application prospect in the scenarios such as super malls, business buildings, downtown, public amenities, etc. The merits of transient near-field microwave imaging such as strong penetrability, high resolution, low power, radiation safety and feeble inference to the existing communication system make it a potential solution to the real-time short-range locating and imaging technologies. However, the imaging area of short-range locating and imaging including the near-field region, the far-field region and the transition region between them, will lead to a huge computational cost for the near-field imaging algorithms, making real-time imaging a challenge. In this thesis, we make a reverse thinking to realize “entire-field” real-time short-range locating and imaging by extending the imaging area of a kind of far-field microwave imaging based on Rotman lens to the near-field region.To extent the imaging area of Rotman lens to the near-field region, several works are done.First, lower return loss of the Rotman lens is achieved by redesigning the taper line based on the theory of small reflection as well as presenting a routing method for big curvature delay line.Second, the reasons for blind near-field region of the Rotman lens are studied, and then a new angle-time spread function(ATSF) is proposed to describe the spread properties of the out-of-focus scatter signals. Based on the ATSF, the out-of-focus scatter signals from the near-field targets are modeled. Two methods to obtain ATSF are presented.Third, based on the idea of localized ATSF, a near-field scatter signal restoration algorithm is proposed to realize Rotman lens near-field imaging without sacrificing its far-field imaging capability. Two methods of dividing the localized imaging area are presented.At last, a Rotman lens near-field transient microwave imaging system is built. The effectiveness of the proposed algorithm is validated by the experiment and simulation. The results show that the angular & radial resolutions of near-field targets are enhanced significantly by the imaging algorithm. The nearer the targets are to the array, the better the targets angular resolution is improved, while the improvement of radial resolution stays consistent as the targets position changes.